*******************************************************************************

	program geomchk 

*******************************************************************************
c
c	To compile non-graphics programs use : 
c        f77 $(OPT) geomchk.f -o geomchk 
c
        real rx(300), ry(300), rz(300)
        real dax,day,daz,dhx,dhy,dhz
        real davec,dhvec,udax,uday,udaz
        real dstart,disp,prod
        character*80    record(300)
        character*80    rec
        character*80    aform
        character*40	fname
        character*40	gname
        character*8     left
        character*30    right 
        integer         i,ia,id,ih
	integer	        natom
c
c 
	 print *,'Enter car file name (inside single quotes): '
	 read(5,*) fname
c
         print *,'Input the number of atoms:'
         read(5,*) natom 
c
c       
         open(unit=7,file=fname,form='formatted',
     $                            status='old',err=990)
c
         aform = "(a5,3(2x,f13.9),a29)"
c
         read(7,'(a80)',end=997,err=995) record(1)
         read(7,'(a80)',end=997,err=995) record(2)
         read(7,'(a80)',end=997,err=995) record(3)
         read(7,'(a80)',end=997,err=995) record(4)

         do 200 i=1,natom
           read(7,'(a80)',end=997,err=995) record(i+4)
           write(6,'(a80)') record(i+4)
           read (record(i+4),aform,err=996) left,rx(i),
     $                       ry(i),rz(i),right
200      continue
         print *,'Input the atom number of end atom#1:'
         read(5,*) id 
         print *,'Input the atom number of end atom#2:' 
         read(5,*) ia 
         print *,'Input the atom number of the center atom:'
         read(5,*) ih 
         dax=rx(id)-rx(ih)
         day=ry(id)-ry(ih)
         daz=rz(id)-rz(ih)
         davec=sqrt(dax*dax+day*day+daz*daz)
         print *,'The center-1 distance is:',davec
         dhx=rx(ia)-rx(ih)
         dhy=ry(ia)-ry(ih)
         dhz=rz(ia)-rz(ih)
         dhvec=sqrt(dhx*dhx+dhy*dhy+dhz*dhz)
         print *,'The center-2 distance is:',dhvec
         prod=(dax*dhx+day*dhy+daz*dhz)/davec/dhvec
         prod=180/3.1415926*acos(prod)
         print *,'The angle between C-1 and C-2 is:',prod
         udax=dax/davec
         uday=day/davec
         udaz=daz/davec
c
         close(7)
c
         goto 999
990      continue
         print *,'Error in input file'
         goto 999
995      continue
         print *,'Error in format'
         print *, record
         goto 999
996      continue
         print *,'Error parsing format'
         print *, record
         print *,left, rx(i), ry(i), rz(i),right 
         goto 999
997      continue
         print *,'End of file detected'
999      continue
c
         end
c